Field of Invention
The present invention is directed to data recording devices, and more particularly to an enclosure that configured to receive external ultrasonic signals, such as the echolocation calls of bats, and to deliver the signals to an ultrasonic microphone.
Discussion of Related Art
There are many applications for automated data collection. In particular, the collection of audio data in the field can be used to monitor populations of wildlife, such as bats, birds, frogs and whales for presence, absence, and abundance data for specific species. Various devices have been created to collect this type of data.
With the increased miniaturization of electronics for consumer devices, a variety of inexpensive SMT (Surface Mount Technology) microphone sensors have been introduced to the market, some suitable for detecting ultrasonic signals. These microphones are designed to be mounted directly on a printed circuit board along with other electronic components using highly automated manufacturing lines. Some of these microphones have top ports, while others have bottom ports. Top port microphones are sensitive to sound waves on the top of the device, that is, on the same side of the printed circuit board as the microphone. Bottom port microphones are mounted over an opening (or via) in the printed circuit board and are sensitive to sound waves on the opposite side of the printed circuit board.
The ultrasonic echolocation calls of bats are typically narrow band, frequency-modulated signals with frequencies of between 20 and 150 kilohertz (noting some bats echolocate at higher and lower frequencies). This corresponds to wavelengths between approximately 0.2 and 1.7 centimeters. When a sound wave encounters an object larger than approximately one quarter wavelength (e.g. as small as 0.05 centimeters), the sound wave can experience a combination of constructive and destructive interference resulting in frequency-dependent distortion of the sound.
Given that a printed circuit board with a surface mounted ultrasonic sensor needs to be enclosed by some kind of housing, it is challenging to design the housing in such a way that an ultrasonic sound wave from outside the housing can reach the sensor with an acceptably low level of distortion. Additionally, the design should be inexpensive to mold and aesthetically pleasing. Mechanical solutions may be constrained by the tolerances of a molding process and can be supplemented with optional electronic solutions to further correct the resulting frequency response of the system.